Liquid containers blow-molded from linear high-density ethylene polymers are easily fabricated at modest cost and have received wide public acceptance as containers for many types of liquid products including distilled water, aqueous hypochlorite bleaches, vinegars, lubricating oils, and the like. Such containers also have been used for packaging of certain types of liquid detergent products. The use of such containers to package liquid detergent products has been somewhat restricted, however, by reason of the fact that many types of liquid detergent products accelerate the tendency of the container to exhibit stress cracking. Stress cracking is evidenced by the appearance of hazy cracks in the container which are aesthetically unpleasing to the ultimate consumer. In extreme cases, stress cracking can lead to leakage of the contents from the container. The stress crack resistance of linear high-density ethylene resins can be improved by blending such resins with other polymers such as butyl rubber, ethylene-propylene copolymer rubbers, and the like. The resulting blends, however, have reduced strength and stiffness and are not suitable for many packaging applications.
For the above reasons, there is need in the art for improved resin formulations containing linear high-density ethylene polymers and having improved resistance to environmental stress cracking. Such improved resin formulations, in addition to having improved resistance to environmental stress cracking, also will be required to maintain to a substantial degree the desirable physical properties of the linear high-density ethylene polymers presently employed in the manufacture of blow-molded containers.